1. Field of the Invention
The present invention relates to a semiconductor device, a display device, and a light-emitting device; and a driving method thereof.
2. Description of the Related Art
Flat panel displays such as liquid crystal displays (LCDs) become widely used in recent years. However, the LCD has various disadvantages such as narrow viewing angle, narrow chromatic range, and slow response speed. Thus, research of an organic EL (also referred to as electroluminescence, organic light-emitting diode, OLED, or the like) display as a display that overcomes those disadvantages becomes active (see Patent Document 1).
However, the organic EL display has a problem in that current characteristics of a transistor for controlling current which flows to an organic EL element vary among pixels. When the current flowing to an organic EL element (i.e., current flowing through a transistor) varies, the luminance of the organic EL element also varies, whereby an image with unevenness is displayed on a screen. Thus, a method for compensating variation in threshold voltage of transistors is examined (see Patent Documents 2 to 6).
However, even if variation in threshold voltage of transistors is compensated, variation in mobility of the transistors leads to variation in current flowing to an organic EL element, so that image unevenness occurs. Thus, a method for compensating not only variation in threshold voltage but also variation in mobility of transistors is examined (see Patent Documents 7 and 8).